This is what I read in the most recent PTR patch notes:
...Any Battle Pet that could be awarded from a Throne of Thunder boss on Raid Finder difficulty can now be won from a bonus roll, in addition to the standard bonus roll reward.
Does this mean that until 5.4, pets aren't able to drop from bonus rolls? I could have sworn we had confirmation of people getting Living Sandling and Son of Animus from bonus rolls.